The present invention relates to a method and system for determining memory deficiency malingering.
It is sometimes required to test a person's memory. For example, occasionally a person who has suffered an accident or head injury asserts that he is experiencing memory problems. This may arise in the context of a claim to an insurance company or in personal injury litigation. In such situations, a memory test may be useful to determine whether the person actually is experiencing memory difficulties or is feigning memory problems for the purpose of financial gain. The feigning or exaggeration of memory impairment by individuals who do not in fact have memory problems is referred to as "malingering".
Various neuropsychological tests have been developed that can be used to assess a person's memory. Some tests are specially designed to test for short term memory deficiencies that may be associated with head injury accidents. The purpose of such tests is to determine whether the subject actually has a memory deficiency or is faking.
A related test is the forced choice procedure test (see, Hiscock & Hiscock "Refining the forced-choice method for the detection of malingering", Journal of Clinical and Experimental Neuropsychology, 11, 967-974, 1989) which is a standard neuropsychologist's pencil-and-paper test involving simple matching-to-sample skills. A commercial computerized form of this test is called the "Multidigit Memory Test," ("MDMT"; see, Nies and Sweet, "Neuropsychological assessment and malingering: A critical review of past and present strategies", Archives of Clinical Neuropsychology, Vol. 9, No. 6, pp. 501-552, Nov. 18, 1994). These tests are directed more to memory deficit malingering than true memory testing, since suspected malingerers, but not real organic amnestics, "do poorly" on them.
In the conventional MDMT, there are 3 blocks of trials. The protocol for each trial in a block is as follows: A subject faces a computer screen. Every 5-20 seconds a 5-digit sample number appears on the screen for about 3 seconds. The sample onset is accompanied by a 2-tone (each an octave apart) signal. Then, there is a delay interval of 2 seconds. (In Block II, the interval is 7 seconds and in Block III, the interval is 15 seconds). This interval is followed by a test to see if the subject remembers the original sample number. That is, there are 3 blocks of 24 trials each, with the first block having a short interval ("easy" task--2 second), the second block being "harder" with 7 second delays, and the third block being "hardest" with 15 second delays.
The test of memory on the conventional MDMT involves presentation on a display screen, after the delay intervals, of the correct 5-digit match on one side (right or left) and a mismatch on the other side, along with instructions to the subject to press one key or another to indicate right or left as his choice of the matching number. The side where the match appears varies randomly across trials. Immediately after the choice, the signal "right" or "wrong" is presented, accompanied by a sustained (about 1 second) high tone for "right," or a rapid (1 second) sequence of 5 low tones for "wrong".
Before the second and third blocks, the subject gets the message "You're doing great, now let's make it harder!" This is really an entrapment attempt, because normal subjects as well as almost all but the most grossly damaged actual but non-malingering head-injured patients perform at near 100% correct on all blocks of this test. However, suspected patient malingerers and experimentally instructed, malingering normal subjects do relatively "poorly" on this test, especially on the "harder" blocks. The blocks are all easy for all persons, even those with head injury.
Other, similar tests for determining simulated memory deficiency include the Fifteen-Item Test and the Hiscock Forced-Choice Procedure. These tests, and others, are described in "Detecting Simulated Memory Impairment: Comparison of the Rey Fifteen-Item Test and the Hiscock Forced-Choice Procedure", Guilmette et al , The Clinical Neuropsychologist, 8, 283-294 (1994).
Although these tests may be useful in many circumstances, they fall short of correctly identifying all malingering subjects with certainty. Neuropsychologists tend to take poor scores (percent correct) on such tests as evidence of malingering. Of course, it is difficult to be absolutely certain that a poor behavioral score provides this evidence, since some legitimately injured person could produce a low score. Thus the test score, by itself, is of limited value. It is typically one of many results which a neuropsychologist, neurologist, or psychiatrist would look at so as to render an opinion about malingering.
Accordingly, there continues to be a need for a highly reliable memory test procedure to determine whether or not a person is malingering memory impairment,